This invention relates to a method and equipment for forming a composite resin material comprising an outer synthetic resin layer and an inner synthetic resin layer enveloped by the outer synthetic resin layer.
A compressed multi-layer molded structure comprising an outer synthetic resin layer and an inner synthetic resin layer enveloped by the outer synthetic resin layer is disclosed in the Japanese Laid-open Patent Publication No. 62-184817. This compressed molded product of multi-layer structure is conveniently used to produce containers, container lids, or liners for containers. In such applications, the outer synthetic resin layer is formed from synthetic resin of a type having superior mechanical and sanitary properties, and the inner synthetic resin layer is formed from synthetic resin of a type having superior gas-barrier and heat-resistance properties.
The foregoing Japanese Patent Laid-open Patent Publication No. 62-184817 discloses a device for forming a composite synthetic resin material in which an inner synthetic resin layer is enveloped by an outer synthetic resin layer. The assembly thus formed is compressed to form the foregoing multi-layer compressed mounding product. This device for forming the composite synthetic resin includes a main channel with a discharge opening at its tip. The synthetic resin for forming the outer synthetic resin layer is fed continuously into the main channel. The inner synthetic resin layer is fed into the main channel through an inflow opening communicating with the main channel. An inner synthetic resin channel communicates with the inflow opening. The inner synthetic resin is fed by intermittently applying pressure to feed the synthetic resin through the inner synthetic resin channel and the intermittent inflow opening, and thence into the continuous flow of outer synthetic resin. A shutter opens and closes the intermittent inflow opening to provide intermittent flow of inner synthetic resin through the intermittent inflow opening. The inner synthetic resin flows under pressure into the outer synthetic resin of the main channel through the inner synthetic resin channel and the intermittent inflow opening. This process deposits inner synthetic resin at intervals in the outer synthetic resin flow. The combined synthetic resin flow is discharged from the discharge opening and cut by a cutting means through portions of the combined synthetic resin flow where the inner synthetic resin is absent. The cutting means includes a cutting edge which is rotated across the composite synthetic resin flow, in the horizontal direction against the direction of running. Thus, separated pieces of the composite synthetic resin material is formed in which inner synthetic resin is enveloped by outer synthetic resin.
Japanese Laid-open Patent Publication No. 1-195016 discloses a device for forming a composite synthetic resin material in which at least the lower channel end thereof is provided with an auxiliary channel surrounding the intermittent inflow opening. The auxiliary channel is elongated in the inside of the circular cross-sectional part of the main channel, to prevent so called threading phenomenon. The threading phenomenon is one in which the inner synthetic resin continues to feed a small amount of inner synthetic resin even after the intermitted inflow member is closed by its shutting member. The small amount of material fed at these times produce elongates thread-like strands even after the intermittent inflow opening is closed. The continued feeding is caused by the composite resin running in the auxiliary channel colliding with the tip of the opening at the shutting member, thereby scratching off some of the remaining inner synthetic resin and adding an unwanted string-like portion to the flow of outer synthetic resin. If the synthetic resin running in the auxiliary channel is identical to the outer synthetic resin running in the main channel, then no difficulty results. However, when the two types of synthetic resin are different is properties or color, the threading phenomenon is a problem.
In the above-described conventional techniques for forming composite synthetic resin materials, and in the device itself, a number of problems remain to be solved.
First, when the composite synthetic resin is produced at a relatively high speed, the threading phenomenon of the inner synthetic resin leaves a relatively long tail in the upstream direction of flow, thereby leaving relatively short lengths of the composite material at which cut can be made without cutting through the inner synthetic resin.
The resulting precision required to cut the composite synthetic resin, without exposing is difficult to achieve and, upon failure to achieve the required precision, the serious possibility exists of producing defective composite synthetic resin materials in which the inner synthetic resin is exposed at the cuts.
The composite synthetic resin is cut by a rotating blade intersecting the flow of the composite synthetic resin exiting the discharge opening. Sometimes, instead of the cut material leaving the cutting edge cleanly, a portion tends to stick to the blade. During subsequent cuts, the material stuck to the blade, partly cooled and hardened during its time on the blade, becomes detached from the blade, and is added to the new material leaving the discharge opening. This produces undesirable unevenness in the cut pieces.